Name:	pfg_CreditDerivativePurchasedCreditProtectionAlternate
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Describes, in the context of the estimate of credit derivatives purchased, the fair value for any purchased credit protection with identical underlying(s).

No definition available.

Name:	pfg_CreditDerivativePurchasedFairValue
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Discloses the notional amount of the credit derivatives sold (or each group of similar credit derivatives) as of the date of the statement of financial position.

No definition available.

Name:	pfg_CreditDerivativeSoldNotional
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the amount of notional of derivatives in consolidated collateralized private investment vehicle VIEs where the credit risk is borne by third-party investors.

No definition available.

Name:	pfg_CreditDerivativeSoldNotionalWhichCreditRiskIsBorneByThirdParty
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Discloses the fair value of the credit derivatives sold (or each group of similar credit derivatives) as of the date of the statement of financial position.

No definition available.

Name:	pfg_CreditDerivativesSoldFairValue
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the weighted-average expected life in years for credit derivatives sold.

No definition available.

Name:	pfg_CreditDerivativesSoldWeightedAverageExpectedLife
Namespace Prefix:	pfg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5708775-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Credit Derivative
-URI http://asc.fasb.org/extlink&oid=6854095

Name:	us-gaap_CreditDerivativeMaximumExposureUndiscounted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_CreditDerivativesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_CreditDerivativesByContractTypeAxis=us-gaap_CreditDefaultSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditDerivativesByContractTypeAxis=pfg_SingleNameCreditDefaultSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsAAARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsAARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsBBBRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsBBRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsCCCRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsCCRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_UnderlyingAssetClassAxis=pfg_GovernmentDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_SovereignDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditDerivativesByContractTypeAxis=us-gaap_CreditIndexProductMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditRatingStandardPoorsAxis=pfg_StandardPoorsNearDefaultRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: